Soy Saponins Kill Colon Cancer Cells in an Intriguing Way

Colon Cancer

Although soy isoflavones get a lot of attention for their health benefits, another soy constituent, soy saponins, has been generating excitement in Keith Singletary's University of Illinois lab.

Saponins protect soybeans from predators and insects, but they may protect people who include soy in their diet from colon cancer as well, according to studies of Singletary's work published in Carcinogenesis.

Allison Ellington, a doctoral student in Singletary's lab, has shown that soy saponins inhibit the growth and development of human colon cancer cells in culture, and she and Singletary are particularly intrigued by the way it all happens.

"Allison has characterized that saponins can stimulate autophagy, a process that causes a type of programmed cell death, in colon cancer cells," said Singletary, a U of I professor of food science and human nutrition.

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"It is becoming increasingly apparent that autophagy, a process of cell death different than the more common death pathway, apoptosis, may contribute to fighting chronic diseases such as cancer," Singletary added. The saponins appear to block certain cancer signaling pathways in the colon cancer cells that control cell survival.

Consuming a serving and a half a day of saponin-rich legumes or legume products, such as soybeans, garbanzo beans, and navy beans, is likely to produce in the digestive tract the same concentrations that produced anti-cancer effects in Singletary's cell cultures.

"Whenever you're talking about a plant chemical or a nutritional compound, you have to ask whether this compound can reach the target tissue. In this case, it appears that soy saponins may actually reach the colon in concentrations that are cancer-preventive," Singletary said.

Both Singletary and Ellington suggest that a fruitful area of future research would be to determine whether soy saponins may act together with other soy constituents, such as the isoflavones or the phytosterols, to enhance colon cancer prevention.

Mark Berhow of the National Center for Agricultural Research Service in Peoria, Illinois, provided purified samples of saponins for the studies, the first of which appeared in the January 2005 issue of Carcinogenesis with a second article to appear in an upcoming issue of Carcinogenesis. Partial funding was provided by a grant from the State of Illinois through the Illinois Council on Food and Agricultural Research (C-FAR). - Urbana